1. Field of the Invention
This invention relates generally to the field of loudspeakers. In particular, the invention relates to a multiple voice-coil cone-driver that may be incorporated into a loudspeaker.
2. Related Art
A loudspeaker typically includes a frame, a magnet assembly that provides a magnetic field across an air gap, a voice-coil, a former for supporting the voice-coil in the air gap, a diaphragm having an outer perimeter and an apex, and a surround coupled to the outer perimeter and the frame to support the outer perimeter from the frame. The voice-coil, supported by the former, is coupled to the apex of the diaphragm so that the current that flows through the voice-coil and causes the voice-coil to move in the air gap also causes the diaphragm to move.
In some settings, it is desirable to extend the upper threshold frequency (also known as “UTF”) of a loudspeaker so that the loudspeaker may more accurately reproduce a wider range of frequency content in speech, music, and the like. At the same time, many applications demand that the loudspeaker remain small in package size. Traditionally, designers extended the upper threshold frequency by decreasing the moving mass (i.e., the physical structure that moves when the voice-coil is energized), increasing the cone depth, or adding an additional cone (e.g., tailored to high frequency response). Unfortunately, these approaches are not always suitable.
For example, decreasing the moving mass often entails lightening the diaphragm, which typically increases distortion. As another example, increasing the cone depth may place the loudspeaker outside of acceptable packaging depth requirements. These requirements may be particularly stringent in, for example, automobile applications.
Therefore, there is a need for extending the upper threshold frequency of a loudspeaker while overcoming the disadvantages associated with decreasing the moving mass, increasing the cone depth and/or adding an additional cone.